This invention relates to optical information recording/reproducing apparatus for recording and reproducing information on and from an optical disc and more particularly to an optical information recording/reproducing apparatus which can afford to detect contaminants on an optical disc.
Because of high convergency of laser beams and narrowness of the pitch between tracks, the optical information recording/reproducing apparatus adapted to record information on an optical disc can provide high recording density which is 10 or more times the recording density obtained with the magnetic disc apparatus.
Especially, a write-once type optical disc and a magneto-optical disc are noticeable for the fact that information can be recorded and reproduced with these discs in contrast to a video disc and a compact disc which are dedicated to reproduction. FIG. 11 schematically shows a prior art optical information recording/reproducing apparatus. Referring to FIG. 11, information is recorded on an optical disc 1 which is rotated by a motor 2. An optical head 3 converges laser beams on the optical disc 1 for the purpose of recording a signal thereon and detecting a change in reflection of a laser beam to read the recorded information. A laser drive head amplifier circuit 4 is comprised of a laser drive unit for driving a laser included in the optical head 3 and a head amplifier for detecting a focus error signal 100, a tracking error signal 101 and a reproduction signal 102. A focus control circuit 5 generates a focus drive signal 106 which drives an actuator of the optical head so that a laser beam can be focused on a guide track on the optical disc 1. A tracking control circuit 6 drives the actuator of the optical head with a tracking drive signal 107 so that the laser beam can follow the guide track on the optical disc 1. A data modem circuit 7 digitally modulates an input data signal 103 and demodulates the reproduction signal 102 to deliver an output data signal 105. A control microcomputer 8 (CPU) performs system control for the apparatus. The microcomputer 8 issues a focus command signal 108 to the focus control circuit 5, a tracking command signal 109 to the tracking control circuit 6 and a command signal 110 to the data modem circuit 7. In the prior art optical information recording/reproducing apparatus constructed as above, laser beams emitted from the optical head 3 are converged on a guide track on the optical disc 1 rotating at a constant speed and a laser beam is caused to follow the track. The focus error signal 100 and the tracking error signal 101 which are detected by the optical head 3 are respectively applied to the focus control circuit 5 and the tracking control circuit 6, whereby the actuator of the optical head 3 is driven for focus/tracking controlling to permit the optical head 3 to irradiate laser beams which are focused on a guide track.
For recording data, the input data signal 103 is modulated by the data modem circuit 7 and laser beams of the intensity suited for recording are modulated with a modulation data signal 104 so as to be irradiated on the optical disc 1.
For reproducing data, laser beams of a low level insufficient for recording are irradiated on the optical disc 1 and a resulting reproduction signal 102 is demodulated by the data modem circuit 7 to produce an output data signal 105. Typically, reproduction power has a level of about 1 mW and recording power has a level of 5 to 10 mW.
With the above construction, however, when the optical disc 1, which is typically rotated at a high speed of about 1800 rpm, is left to rotate for a long period of time during a continuous operation, dusts in the air are deposited onto the surface of the optical disc 1 because the optical disc 1 having a substrate made of an electrically insulating material such as resin or glass is electrified. The laser beams are partly absorbed and scattered by the deposited dusts and power of the laser beams is considerably attenuated by several of tens of percents. Consequently, when recording a signal on a recording layer of a photosensitive material which is vapor-deposited on a guide track, the requisite level of recording laser power, exemplarily 5 to 10 mW, becomes considerably deficient amounting to 3 to 6 mW, thus preventing excellent recording of the signal.
In other words, since recording is not effected with an optimum level of recording power and so record of pits are not saturated, there result problems that the recording pits are degraded under the influence of a change in environment to decrease their life and that the amplitude of the reproduction signal is decreased, thus aggravating the bit error rate.